hen a disease swept through southern China last year, killing off nearly 25,000 piglets over a period of months, scientists initially thought a diarrheal virus was to blame. They later determined it was something else: a dangerous coronavirus, the same family of viruses that 15 years ago caused a human epidemic of SARS, or severe acute respiratory syndrome.

Scientists who went looking for those viruses in bats in China’s Guangdong and Yunnan provinces had found dozens that are closely related to the SARS coronavirus. In some places, they found people living nearby who had antibodies to these viruses, suggesting they had been previously infected.

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